Combustion device

ABSTRACT

The present invention provides a combustion device. In ON-OFF combustion control processing for intermittently performing the combustion operation of burners ( 4 ), a control unit ( 30 ) of a combustion device (water heater) ( 1 ), which includes the burners ( 4 ), a fuel supply unit ( 5 ), and a combustion fan ( 10 ), controls the fuel supply unit ( 5 ) and the combustion fan ( 10 ) so as to change the amount of a fuel to be supplied to the burners ( 4 ) and the number of rotations of the combustion fan ( 10 ) according to a required amount of heat for the temperature control of a target fluid (water for hot water supply) when the burners ( 4 ) are ignited to restart a combustion operation after the burners ( 4 ) are extinguished.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a combustion device such as a water heater and a heating device.

2. Description of the Related Art

As a combustion device adapted to heat a target fluid subject to temperature control, such as water for hot water supply or water for heating, by using the combustion heat of a burner so as to maintain the temperature of the fluid at a temperature in the vicinity of a required target temperature, there has conventionally been known a combustion device that intermittently performs the combustion operation of a burner (the combustion operation and the suspension thereof being alternately repeated) when a required amount of heat necessary for the temperature control of a target fluid is small, as seen, for example, in Japanese Utility Model Application No. 59-23555 (hereinafter referred to as Patent Document 1) or Japanese Patent Application Laid-Open No. 2020-29971 (hereinafter referred to as Patent Document 2). Hereinafter, the control for intermittently performing the combustion operation of a burner as described above may be referred to as “the ON-OFF combustion control” of the burner.

According to the technologies described in Patent Documents 1 and 2, in the ignition processing for restarting the combustion operation of the burner while the ON-OFF combustion control of the burner is being carried out, the amount of a fuel to be supplied to the burner and the number of rotations of a combustion fan for supplying air for combustion to the burner are controlled independently of a required amount of heat for the temperature control of a target fluid. For this reason, the amount of combustion heat generated by the burner at the time of ignition to restart the combustion operation of the burner or immediately after the ignition tends to be excessive or insufficient with respect to the required amount of heat.

In this case, if the amount of heat generated at the time of ignition of the burner or immediately after the ignition is larger than the required amount of heat, then the temperature of a target fluid is apt to overshoot a required target temperature and the number of rotations of a combustion fan is higher than necessary, thus frequently causing the operation sound of the combustion fan to become a noise.

On the other hand, if the amount of heat generated at the time of ignition of the burner or immediately after the ignition is smaller than the required amount of heat, then the rise of the temperature of the target fluid tends to be delayed or ignition failure frequently tends to occur.

SUMMARY OF THE INVENTION

The present invention has been made in view of the background described above, and an object of the invention is to provide a combustion device capable of properly performing the ignition of a burner in the ON-OFF combustion control of the burner in a manner suited for the temperature control of a target fluid.

To this end, a combustion device in accordance with the present invention includes: a burner which generates heat for heating a target fluid by a combustion operation; a fuel supply unit which supplies a fuel to the burner; a combustion fan which supplies air for combustion to the burner; and a control unit which has a function for determining a required amount of heat for temperature control of the target fluid and for controlling the fuel supply unit and the combustion fan according to the required amount of heat,

wherein the control unit is configured to be capable of performing ON-OFF combustion control processing, which is processing for controlling the fuel supply unit and the combustion fan so as to intermittently perform the combustion operation of the burner, and is also configured to control the fuel supply unit and the combustion fan so as to change an amount of a fuel to be supplied to the burner and a number of rotations of the combustion fan according to a required amount of heat for temperature control of the target fluid at the time of igniting the burner to restart the combustion operation of the burner after the burner is extinguished in the ON-OFF combustion control processing (a first aspect of the invention).

In the present invention, the term “temperature control” of a target fluid means to control the temperature of the target fluid such that the temperature coincides or substantially coincides with a required target temperature.

According to the first aspect of the invention, in the ON-OFF combustion control processing, the fuel supply unit and the combustion fan are controlled such that the amount of a fuel to be supplied to a burner and the number of rotations of the combustion fan change according to the required amount of heat for the temperature control of a target fluid when the burner is ignited to restart the combustion operation of the burner after the burner is extinguished. This enables the ignition of the burner that can prevent the temperature of the target fluid from overshooting a required target temperature or prevent a delay in a temperature rise of the target fluid at the time of ignition of the burner or immediately after the ignition.

Further, when the burner is ignited after being extinguished, the required amount of heat of the burner does not increase much, so that the number of rotations of the combustion fan at the time of ignition can be suppressed to a small number of rotations, thus making it possible to suppress the operation sound of the combustion fan when igniting the burner.

Consequently, according to the first aspect of the invention, the ignition of a burner in the ON-OFF combustion control of the burner can be properly performed in a manner suited to the temperature control of a target fluid.

In the aforesaid first aspect of the invention, preferably, the control unit has a function for detecting a degree of blockage of a supply/exhaust flow path, which is a flow path of air for combustion or combustion exhaust gas, while operating the combustion fan at a predetermined number of rotations in an extinguished state of the burner in the ON-OFF combustion control processing, and is configured to control the combustion fan so as to change the number of rotations of the combustion fan at the time of ignition following the extinguished state of the burner according to a required amount of heat for the temperature control of the target fluid and the degree of blockage in the case where at least the degree of blockage is higher than a predetermined value (a second aspect of the invention).

With this arrangement, the degree of blockage of the supply/exhaust flow path can be properly detected using various publicly known techniques by operating the combustion fan at a predetermined number of rotations in the extinguished state of the burner in the ON-OFF combustion control processing. Further, if at least the degree of blockage is higher than a predetermined value, then air for combustion in an amount that meets a required amount of heat can be supplied to the burner by controlling the combustion fan as described above, compensating for an influence whereby the amount of air for combustion to be supplied to the burner tends to decrease as the degree of blockage of the supply/exhaust flow path increases. Therefore, even if the blockage of the supply/exhaust flow path progresses to a certain degree, the burner can be satisfactorily ignited with a proper required amount of heat.

In the aforesaid first aspect of the invention, a mode may be adopted, in which the control unit has a function for detecting the degree of blockage of the supply/exhaust flow path, which is the flow path of air for combustion or combustion exhaust gas, while operating the combustion fan at a predetermined number of rotations in the extinguished state of the burner in the ON-OFF combustion control processing, and is configured to control, in the case where the degree of blockage is lower than a predetermined value, the fuel supply unit and the combustion fan so as to change the amount of a fuel to be supplied to the burner and the number of rotations of the combustion fan according to a required amount of heat for the temperature control of the target fluid at the time of igniting the burner to restart the combustion operation of the burner after the burner is extinguished, and to control, in the case where the degree of blockage is higher than a predetermined value, the fuel supply unit so as to set the amount of a fuel to be supplied to the burner at the time of igniting the burner to restart the combustion operation of the burner after the burner is extinguished to a predetermined amount, and to control the combustion fan so as to set the number of rotations of the combustion fan to a number of rotations set according to the degree of blockage (a third aspect of the invention).

With this arrangement, as with the second aspect of the invention, the degree of blockage of the supply/exhaust flow path can be properly detected using various publicly known techniques by operating the combustion fan at a predetermined number of rotations in the extinguished state of the burner in the ON-OFF combustion control processing. Further, when the degree of blockage is lower than a predetermined value, the effect described in the first aspect of the invention can be obtained by controlling the fuel supply unit and the combustion fan as with the first aspect of the invention.

Further, if the degree of blockage of the supply/exhaust flow path is higher than a predetermined value, then the fuel supply unit is controlled to set the amount of a fuel, which is supplied to the burner at the time of igniting the burner when restarting the combustion operation of the burner after the burner is extinguished, to a predetermined amount, and the combustion fan is controlled to set the number of rotations of the combustion fan to a number of rotations set according to the degree of blockage, thereby making it possible to stably and satisfactorily ignite the burner, compensating for the influence that the amount of air for combustion to be supplied to the burner tends to decrease as the degree of blockage of the supply/exhaust flow path increases.

In the first aspect of the invention, the control unit is preferably configured to control, in the case where the ignition of the burner is not detected at the time of igniting the burner to restart the combustion operation of the burner after the burner is extinguished, the fuel supply unit and the combustion fan so as to increase the amount of a fuel to be supplied to the burner and the number of rotations of the combustion fan as compared with the time of ignition at which the ignition was not detected (a fourth aspect of the invention). The same applies to the second aspect of the invention and the third aspect of the invention described above (a fifth aspect of the invention and a sixth aspect of the invention).

With this arrangement, if a misfire occurs due to ignition failure at the time of ignition after the burner is extinguished in the ON-OFF combustion control processing, then the amount of a fuel to be supplied to the burner and the number of rotations of the combustion fan are increased before reigniting the burner, so that the reliability of proper ignition of the burner by the reignition can be enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically illustrating the overall configuration of a water heater as an example of a combustion device of an embodiment;

FIG. 2 is a flowchart illustrating the processing in a first embodiment of the control unit illustrated in FIG. 1; and

FIG. 3 is a flowchart illustrating the processing in a second embodiment of the control unit illustrated in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

A first embodiment of the present invention will be described below with reference to FIG. 1 and FIG. 2. Referring to FIG. 1, a water heater 1 of the present embodiment has a heat source unit 2 installed outdoors. A combustion casing 3 having a combustion chamber 3 a formed therein is installed in the heat source unit 2. Burners 4 as heating units are disposed at a lower part of the combustion chamber 3 a in the combustion casing 3.

The burners 4 are gas burners in the present embodiment. The burners 4 are composed of a plurality of burners, e.g., three types of burners, namely, first burners 4 a, second burners 4 b, and third burners 4 c that can separately perform a combustion operation. In the illustrated example, the first burners 4 a, the second burners 4 b, and the third burners 4 c have different combustion areas from each other. However, the combustion area of each of two or more burners constituting the burners 4 may be the same.

The heat source unit 2 includes a fuel supply unit 5 for supplying a fuel gas to the burners 4. The fuel supply unit 5 has a main gas supply line 6, to which a fuel gas is supplied from a gas supply source (not illustrated) and three secondary gas supply lines 6 a. 6 b, and 6 c branched from the main gas supply line 6. Each of the secondary gas supply lines 6 a, 6 b, and 6 c is introduced into the combustion chamber 3 a from outside the combustion casing 3 such that a fuel gas can be supplied separately to the first burners 4 a, the second burners 4 b, and the third burners 4 c.

The fuel supply unit 5 further includes a main valve 7 interposed in the main gas supply line 6 such that the main gas supply line 6 can be opened and closed, a gas amount regulating valve 8 interposed in the main gas supply line 6 such that the amount of a fuel gas to be supplied to the burners 4 can be adjusted, and switching valves 9 a, 9 b, and 9 c interposed in the secondary gas supply lines 6 a. 6 b, and 6 c, respectively, such that each of the secondary gas supply lines 6 a. 6 b, and 6 c can be opened and closed. Each of the main valve 7 and the switching valves 9 a. 9 b, and 9 c is composed of, for example, a solenoid valve. The gas amount regulating valve 8 is composed of, for example, a proportional valve or an electric flow control valve.

In the present embodiment, the fuel supply unit 5 is configured as described above, so that the total amount of combustion heat of the burners 4 can be changed over an extensive range by changing the combination of the open/closed state of each of the switching valves 9 a. 9 b, and 9 c, with the main valve 7 controlled to be open, when performing the combustion operations of the burners 4. The burners 4 are not limited to burners composed of a plurality of burners, the combustion operations of which can be separately performed, and may be configured such that all of the burners 4 perform combustion operations at the same time. In other words, a fuel gas may be supplied from a single gas supply line to all of the burners 4.

Further, the heat source unit 2 includes an electric combustion fan 10 as an air blower for supplying air for combustion to the burners 4. The combustion fan 10 is installed at the bottom of the combustion casing 3 such that outside air serving as the air for combustion can be taken in and the air taken in can be supplied to the burners 4 (all the first to the third burners 4 a, 4 b and 4 c) by the rotation operation of the combustion fan 10. In addition, the amount of the air for combustion to be supplied to the burners 4 can be changed by variably controlling the number of rotations (rotation speed) of the combustion fan 10.

An exhaust port 3 b for exhausting the combustion exhaust gas of the burners 4 from the combustion chamber 3 a is opened at an upper part of the combustion casing 3. The exhaust port 3 b is in communication with the outside of the heat source unit 2 through an exhaust passage (not illustrated). Further installed to the combustion casing 3 are an ignition electrode 12 that generates a spark discharge to ignite the burners 4 by activating an igniter (not illustrated) mounted on the heat source unit 2, and a flame detection sensor 13 for detecting the presence of a combustion flame of the burners 4. The flame detection sensor 13 is composed of, for example, a flame rod, a thermocouple, or the like.

The heat source unit 2 is provided with a configuration related to the water flow for the water for hot water supply as a target fluid (fluid to be heated) in addition to the aforesaid configuration related to the combustion operation of the burners 4. More specifically, the combustion chamber 3 a in the combustion casing 3 is provided with a heat exchanger 21 placed such that the heat exchanger 21 can be heated by the combustion heat of the burners 4. Further, a water flow passage 22 through which water can flow via the heat exchanger 21 is provided.

The water flow passage 22 is connected to the inlet of a water flow passage 21 a of the heat exchanger 21, and includes a water supply passage 22 a through which water for hot water supply is supplied from a water supply source (not illustrated), a hot water supply passage 22 b connected to the outlet of the water flow passage 21 a of the heat exchanger 21, and a bypass passage 22 c that connects the water supply passage 22 a to the hot water supply passage 22 b such that the water for hot water supply can be circulated to the hot water supply passage 22 b from the water supply passage 22 a, bypassing the heat exchanger 21. Further, the downstream side of the hot water supply passage 22 b is disposed such that the water for hot water supply can be supplied to a hot water supply target (a faucet or the like), which is not illustrated, in a kitchen, a washroom, a bathroom, or the like.

Thus, the water flow passage 22 is configured such that the hot water obtained by combining, in the hot water supply passage 22 b, the water for hot water supply that has been heated passing through the heat exchanger 21 from the water supply passage 22 a, and the water for hot water supply passing through the bypass passage 22 c from the water supply passage 22 a can be supplied from the hot water supply passage 22 b to a hot water supply target during the combustion operation of the burners 4.

In the water supply passage 22 a, an electric water amount control valve 23 for adjusting the supply water flow rate, which is the flow rate of water flow of the water supply passage 22 a, and a water amount sensor 24 that detects the supply water flow rate are provided on the upstream side of a branched part of the bypass passage 22 c. Further, the hot water supply passage 22 b is provided with a temperature sensor 25 that detects a hot water supply temperature, which is the temperature of water for hot water supply to be supplied to a hot water supply target (the temperature of hot water flowing toward the downstream side from a part connecting the bypass passage 22 c and the hot water supply passage 22 b), and a temperature sensor 26 that detects the temperature of heat exchanger discharged hot water, which is the temperature of the water for hot water supply that flows out from the heat exchanger 21 to the hot water supply passage 22 b.

A control valve for adjusting the ratio between the flow rate of the water for hot water supply flowing via the bypass passage 22 c and the flow rate of the water for hot water supply that passes through the water flow passage 21 a of the heat exchanger 21 (so-called bypass ratio) may be provided at, for example, a part connecting the bypass passage 22 c and the water supply passage 22 a or the hot water supply passage 22 b, or in the middle of the bypass passage 22 c. Further, one or both of the water amount control valve 23 and the water amount sensor 24 may be provided, for example, in the hot water supply passage 22 b on the downstream side with respect to the part connecting the hot water supply passage 22 b and the bypass passage 22 c.

A description will now be given of the configuration related to the operation control of the water heater 1 (including the combustion operation control of the burners 4). The water heater 1 includes a control unit 30 having a function for controlling the operation thereof, and a remote controller 40 for operating the water heater 1.

The remote controller 40 is a terminal installed in a kitchen, bathroom, or the like, and is provided with a plurality of operation switches, indicators, and the like (not illustrated). The remote controller 40 may have a publicly known configuration. By operating the operation switches of the remote controller 40, it is possible to perform operations, including the turning ON/OFF of the hot water supply of the water heater 1, and setting the target value of a hot water supply temperature (hereinafter referred to as a target hot water supply temperature). The water heater 1 may be provided with a plurality of remote controllers including the remote controller 40.

The control unit 30 is composed of one or more electronic circuit units that include processors, such as microcomputers, memories (RAMs. ROMs. and the like), interface circuits, and the like (not illustrated), and is installed in the heat source unit 2. The control unit 30 is capable of communicating with the remote controller 40 in a wired or wireless manner, and receives the operation information of the remote controller 40 (on/off signals of the hot water supply operation, set values of the target hot water supply temperature, and the like) by this communication. In addition, the control unit 30 receives the detection signals of sensors (including the flame detection sensor 13, the water amount sensor 24, and temperature sensors 25 and 26 described above) provided in the water heater 1.

Further, the control unit 30 has a function for controlling the combustion operation of the burners 4 as a function for implementing one or both of installed hardware configuration and program (software configuration). The combustion operation of the burners 4 is controlled through the main valve 7, the gas amount regulating valve 8, the switching valves 9 a. 9 b, and 9 c, and the combustion fan 10 and through the operation control of an ignitor (not illustrated).

The operation of the water heater 1 of the present embodiment will now be described. The control unit 30 monitors the presence of a water flow in the water flow passage 22 on the basis of an output of the water amount sensor 24, and causes the burners 4 to perform the combustion operation upon detection of the occurrence of a water flow of a predetermined flow rate or more in the water flow passage 22. In this case, the control unit 30 performs the temperature control of the water for hot water supply such that the hot water supply temperature detected by the temperature sensor 25 coincides or substantially coincides with a target hot water supply temperature set by the remote controller 40 by controlling the combustion heat amount of the burners 4 after igniting the burners 4.

In the temperature control, the control unit 30 selectively performs continuous combustion control processing as the control processing for continuously performing the combustion operation of the burners 4 and the ON-OFF combustion control processing as the control processing for intermittently performing combustion operation of the burners 4 (alternately repeating the combustion operation of the burners 4 and the suspension thereof).

According to the present embodiment, the control unit 30 performs the continuous combustion control processing if, for example, a set target hot water supply temperature is a predetermined temperature or higher, or the required amount of heat, which indicates the required value of the combustion heat amount of the burners 4 for the temperature control of the water for hot water supply is a predetermined value or more. Further, the control unit 30 performs the ON-OFF combustion control processing if a set target hot water supply temperature is lower than a predetermined temperature, or the required amount of heat of the burners 4 for the temperature control of the water for hot water supply is lower than a predetermined value.

In the continuous combustion control processing, the control unit 30 sequentially determines, after the burners 4 are ignited, the required amount of heat of the burners 4 primarily on the basis of the detection values of the temperature of the water for hot water supply detected by the temperature sensors 25 and 26, and the detection value of the flow rate of the water flow for hot water supply detected by the water amount sensor 24, performs control of opening/closing the switching valves 9 a, 9 b, and 9 c of the fuel supply unit 5 according to the determined required amount of heat, and also controls the amount of a fuel gas and the amount of air for combustion to be supplied to the burners 4 so as to achieve the required amount of heat by the combustion operation of the burners 4 at a required air-fuel ratio. In this case, the supply amount of a fuel gas is controlled by controlling the gas amount regulating valve 8, and the supply amount of the air for combustion is controlled by controlling the number of rotations of the combustion fan 10.

Meanwhile, the ON-OFF combustion control processing is performed according to the flowchart of FIG. 2 if a water flow (a water flow of a predetermined flow rate or more) in the water flow passage 22 is started in a state in which the target hot water supply temperature has been set to be lower than a predetermined temperature, or if the target hot water supply temperature is changed to a temperature that is lower than a predetermined temperature during the combustion operation of the burners 4 by the continuous combustion control processing, or if the required amount of heat of the burners 4 becomes lower than a predetermined value due to a change of the target hot water supply temperature, or the like.

More specifically, the control unit 30 determines in STEP1 whether the burners 4 are performing the combustion operation, and if a result of the determination is affirmative, then the control unit 30 performs the processing from STEP13, which will be described later. Further, if the result of the determination in STEP1 is negative, then the control unit 30 sequentially repeats in STEP2 the processing for determining whether there is a request for igniting the burners 4 until the determination result becomes affirmative.

In this case, for example, if it is confirmed that the water heater 1 has no abnormality in initial check processing immediately after a water flow of a predetermined flow rate or more is started in the water flow passage 22, then the determination result of STEP2 becomes affirmative. At this time, the control unit 30 drives, in STEP3, the combustion fan 10 at a predetermined small number of rotations for purging the combustion chamber 3 a. Then, the control unit 30 determines whether the degree of blockage of the supply/exhaust flow path (the air supply path or the exhaust path) in communication with the combustion chamber 3 a is higher than a predetermined threshold value while the combustion fan 10 is operating.

Here, according to the present embodiment, the control unit 30 acquires, in STEP4, a detection value of a fan current, which is the energizing current of an electric motor (not illustrated) that drives the combustion fan 10 through a current sensor (not illustrated) as an index value that indicates the degree of blockage of the supply/exhaust flow path. The detection value of the fan current decreases as the degree of blockage of the supply/exhaust flow path increases. Further, if the detection value of the fan current is smaller than a predetermined value, then the control unit 30 determines that the determination result of STEP4 is affirmative, and if the detection value of the fan current is equal to or greater than the predetermined value, then the control unit 30 determines that the determination result of STEP4 is negative.

Whether the degree of blockage of the supply/exhaust flow path is high or low may be determined using other methods. For example, the air volume or pressure in the supply/exhaust flow path can be detected, and the degree of blockage of the supply/exhaust flow path can be determined by using the detection values.

If the determination result of STEP4 is negative, then in STEP5, the control unit 30 calculates the required amount of heat of the burners 4 for the temperature control of the water for hot water supply and also determines, according to the required amount of heat, the ignition number of rotations for the ON-OFF combustion, which is a target number of rotations of the combustion fan 10 when igniting the burners 4 while the ON-OFF combustion control processing of the burners 4 is being performed. The ignition number of rotations for the ON-OFF combustion is determined on the basis of the required amount of heat by using a map prepared in advance or an arithmetic expression. In this case, the ignition number of rotations for the ON-OFF combustion is determined such that the ignition number of rotations increases within the range from a predetermined lower limit value to a predetermined upper limit value as the required amount of heat increases.

The control unit 30 further determines in STEP7 whether the burners 4 were burning immediately before (in other words, whether the burners 4 were in suspension of the combustion operation in the ON-OFF combustion control processing). In this case, the determination result of STEP7 becomes negative when the first (initial) combustion operation of the burners 4 is started in the ON-OFF combustion control processing. At this time, the control unit 30 performs the ignition processing of the burners 4 in STEP8.

In the ignition processing, the control unit 30 activates the combustion fan 10 at a normal ignition number of rotations. The normal ignition number of rotations is the same as the number of rotations of the combustion fan 10 in the ignition processing of the burners 4 when the continuous combustion control processing is started. The number of rotations is a predetermined number of rotations established in advance and lies between a number of rotations corresponding to a minimum required amount of heat and a number of rotations corresponding to a maximum required amount of heat in the continuous combustion control processing.

In the ignition processing of STEP8, the control unit 30 further activates an ignitor (not illustrated) while performing the control for opening the main valve 7 and the switching valve 9 a and the control of the gas amount regulating valve 8 so as to supply a fuel gas in a predetermined flow rate corresponding to the normal ignition number of rotations of the combustion fan 10 to predetermined burners for the ON-OFF combustion control processing, e.g., the first burners 4 a, among the burners 4. In this case, a control value of the gas amount regulating valve 8 that corresponds to the fuel gas in the predetermined flow rate is established in advance.

Thus, a spark discharge is generated at the ignition electrode 12 to ignite the burners 4 while the air for combustion in a flow rate corresponding to the normal ignition number of rotations of the combustion fan 10 and a fuel gas in a flow rate corresponding to the ignition number of rotations are being supplied to the burners 4.

Further, the determination result of STEP7 becomes affirmative at a start of the combustion operation of the burners 4 in each cycle from the second time and after in the ON-OFF combustion control processing. At this time, the control unit 30 performs the ignition processing of the burners 4 in STEP9.

In the ignition processing, the control unit 30 activates the combustion fan 10 at the ignition number of rotations for the ON-OFF combustion determined in STEP5. Further, the control unit 30 activates the ignitor (not illustrated) while performing the control for opening the main valve 7 and the switching valve 9 a and the control of the gas amount regulating valve 8 so as to supply the fuel gas in the flow rate corresponding to the ignition number of rotations for the ON-OFF combustion of the combustion fan 10 to the burners (the first burners 4 a) for the ON-OFF combustion control processing among the burners 4. In this case, the control value of the gas amount regulating valve 8 corresponding to the flow rate of the fuel gas to be supplied to the burners 4 is determined by a map, an arithmetic expression, or the like according to the ignition number of rotations for the ON-OFF combustion of the combustion fan 10 or the required amount of heat of the burners 4.

Thus, a spark discharge is generated at the ignition electrode 12 to ignite the burners 4 while the air for combustion in a flow rate corresponding to the ignition number of rotations for the ON-OFF combustion of the combustion fan 10 and a fuel gas in a flow rate corresponding to the ignition number of rotations are being supplied to the burners 4. The flow rates of the air for combustion and the fuel gas to be supplied to the burners 4 in the ignition processing of STEP9 are smaller than the flow rates of the air for combustion and the fuel gas to be supplied to the burners 4 in the ignition processing of STEP8.

If the determination result of the aforesaid STEP4 is affirmative (if it is determined that the degree of blockage of the supply/exhaust flow path is higher than a predetermined threshold value), then the control unit 30 determines, in STEP6, an ignition number of rotations obtained by correcting the normal ignition number of rotations of the combustion fan 10 described above according to the degree of blockage of the supply/exhaust flow path (a detection value of the fan current as an index value indicating the degree of blockage in the present embodiment).

In this case, the control unit 30 corrects the normal ignition number of rotations according to a detection value of the fan current so as to increase the ignition number of rotations after the correction to be greater than the normal ignition number of rotations as the degree of blockage of the supply/exhaust flow path increases (as the detection value of the fan current decreases). As a method for the correction, for example, the method disclosed by the applicant of the present application in Japanese Patent Application Laid-Open No. 2017-129313 can be adopted.

Then, the control unit 30 further performs the ignition processing of the burners 4 in STEP10. In the ignition processing, the control unit 30 activates the combustion fan 10 at the corrected ignition number of rotations determined in STEP6. Further, the control unit 30 activates an ignitor (not illustrated) while performing the control for opening the main valve 7 and the switching valve 9 a and the control of the gas amount regulating valve 8 so as to supply the fuel gas in the flow rate corresponding to the normal ignition number of rotations of the combustion fan 10 (the fuel gas in the same flow rate as that of the ignition processing in STEP8) to the burner for the ON-OFF combustion control processing (the first burners 4 a) among the burners 4. In this case, the control value of the gas amount regulating valve 8 that corresponds to the flow rate of the fuel gas to be supplied to the burners 4 is the same as the control value in STEP8. Thus, a spark discharge is generated at the ignition electrode 12 to ignite the burners 4 while the air for combustion and the fuel gas in the flow rates equivalent to those of the ignition processing in STEP8 are being supplied to the burners 4.

The control unit 30 determines in STEP11 whether the burners 4 have been ignited on the basis of an output of the flame detection sensor 13 while performing the ignition processing in STEP8 or STEP9 or STEP10 as described above. Further, if the determination result of STEP1 is negative, then the control unit 30 increases the ignition number of rotations of the combustion fan 10 by a predetermined amount from a current number of rotations and performs the ignition processing of the burners 4 again in STEP12. Further, the control unit 30 performs the determination processing of STEP11. In this case, the control unit 30 controls the gas amount regulating valve 8 so as to also increase the amount (the flow rate) of the fuel gas to be supplied to the burners 4 (the first burners 4 a) by a predetermined amount in STEP12.

If the ignition of the burners 4 is not detected in STEP11 even after the ignition processing in STEP12 is performed by a predetermined number of times, then the control unit 30 suspends the control of the combustion operation of the burners 4 and outputs information indicating the occurrence of an abnormality through the remote controller 40.

If the burners 4 are ignited and the determination result of STEP11 becomes affirmative (if the combustion operation of the burners 4 is started by the ignition processing of any one of STEPs 8, 9, 10, and 12), or if the determination result of STEP1 is affirmative (if the burners 4 are already in the combustion operation), then the control unit 30 sequentially performs, in STEP13, the processing for determining whether the hot water supply temperature detected by the temperature sensor 25 has increased to a temperature that is higher than a first threshold value temperature TH1, which has been set to be higher than a target hot water supply temperature by a predetermined value, until the determination result becomes affirmative.

Further, if the determination result of STEP13 becomes affirmative, then the control unit 30 performs the extinguishment processing of the burners 4 (the first burners 4 a) and also drives the combustion fan 10 at a predetermined small number of rotations for purging the combustion chamber 3 a in STEP14. In this case, in the extinguishment processing of the burners 4, the control unit 30 performs the control for closing the switching valve 9 a (or the main valve 7) corresponding to the first burners 4 a, which perform the combustion operation in the ON-OFF combustion control processing, thereby cutting off the supply of the fuel gas to the first burners 4 a.

Further, while operating the combustion fan 10 at the small number of rotations for purging as described above, the control unit 30 sequentially performs, in STEP15, the processing for determining whether the hot water supply temperature detected by the temperature sensor 25 has decreased to a temperature that is lower than a second threshold value temperature TH2, which has been set to be lower than the target hot water supply temperature by a predetermined value, until the determination result becomes affirmative. Further, if the determination result of STEP15 becomes affirmative, then the control unit 30 restarts the processing from the aforesaid STEP4.

In the present embodiment, the ON-OFF combustion control processing is performed as described above. In this case, if the degree of blockage of the supply/exhaust flow path is low, then control is performed such that the ignition number of rotations of the combustion fan 10 and the amount (the flow rate) of the fuel gas to be supplied to the burners 4 in the ignition processing of the burners 4 from the second time and after changes according to the required amount of heat of the burners 4 (increases as the required amount of heat increases). As a result, it is possible to suppress the occurrence of overshoot of the hot water supply temperature with respect to a target hot water supply temperature or excessive delay of temperature rise to the target hot water supply temperature. Consequently, the hot water supply temperature can be stably maintained at a temperature in the vicinity of the target hot water supply temperature.

Further, in the ignition processing of the burners 4 from the second time and after, the required amount of heat of the burners 4 is normally small, so that the ignition number of rotations of the combustion fan 10 in the ignition processing can be suppressed to a lower number of rotations. Consequently, the operation sound of the combustion fan 10 in the ignition processing of the burners 4 from the second time and after can be suppressed.

Further, if the degree of blockage of the supply/exhaust flow path is high, then the ignition processing in STEP10 is performed, so that the reliability of the ignition of the burners 4 being properly performed can be enhanced.

In addition, if the ignition of the burners 4 is not detected in STEP11, then the number of rotations of the combustion fan 10 and the amount of the fuel gas to be supplied to the burners 4 are increased before the ignition processing of the burners 4 is performed again, so that the reliability of the reignition of the burners 4 being properly performed can be enhanced.

Second Embodiment

A description will now be given of a second embodiment of the present invention with reference to FIG. 3. The present embodiment differs from the first embodiment only partly in the control processing by a control unit 30, so that the same matters as those of the first embodiment will not be described.

In the present embodiment, the ON-OFF combustion control processing by the control unit 30 is performed as illustrated by the flowchart of FIG. 3. In this case, according to the present embodiment, if the determination result of STEP4 is affirmative (if the degree of blockage of the supply/exhaust flow path is higher than a predetermined threshold value), then the control unit 30 performs the processing of STEP6 x instead of the processing of STEP6 and STEP10 in the first embodiment, and then performs the processing from STEP7 as with the first embodiment.

In the aforesaid STEP6 x, the control unit 30 determines the ignition number of rotations for the ON-OFF combustion according to the required amount of heat of the burners 4 for the temperature control of the water for hot water supply and the degree of blockage of the supply/exhaust flow path. More specifically, the control unit 30 determines a reference ignition number of rotations for the ON-OFF combustion by the same processing as the processing of STEP5. Further, the control unit 30 corrects the reference ignition number of rotations according to the degree of blockage of the supply/exhaust flow path (according to the detection value of a fan current in the present embodiment), thereby determining the ignition number of rotations used for the actual control of the combustion fan 10. In this case, the ignition number of rotations is corrected such that a corrected ignition number of rotations will be a number of rotations that is higher than the reference ignition number of rotations as the degree of blockage of the supply/exhaust flow path becomes higher.

In STEP6 x, the ignition number of rotations of the combustion fan 10 may alternatively be determined by using a map or the like on the basis of the required amount of heat of the burners 4 and the degree of blockage of the supply/exhaust flow path (the detection value of a fan current in the present embodiment).

The present embodiment is the same as the aforesaid first embodiment except for the matters described above. According to the present embodiment, the amount (the flow rate) of the fuel gas to be supplied to the burners 4 and the number of rotations of the combustion fan 10 at the time of ignition of the burners 4 from the second time and after in the ON-OFF combustion control processing are controlled to a supply amount and a number of rotations that meet a required amount of heat of the burners 4 not only in the case where the degree of blockage of the supply/exhaust flow path is low but also in a situation in which the degree of blockage becomes higher to a certain degree.

Consequently, the hot water supply temperature can be stably maintained at a temperature in the vicinity of a target hot water supply temperature, and the operation sound of the combustion fan 10 at the time of ignition from the second time and after in the ON-OFF combustion control processing can be suppressed. Further, in a state in which the degree of blockage of the supply/exhaust flow path becomes higher to a certain degree, the ignition number of rotations of the combustion fan 10 is set to a number of rotations obtained by correcting the reference ignition number of rotations as described above. This makes it possible to satisfactorily ignite the burners 4 from the second time and after, as with the case where the degree of blockage of the supply/exhaust flow path is low.

In addition, if the ignition of the burners 4 is not detected in the aforesaid STEP11, then the number of rotations of the combustion fan 10 and the amount of a fuel gas to be supplied to the burners 4 are increased before the ignition processing of the burners 4 is performed again, as with the first embodiment, so that the reliability of the burners 4 being properly reignited can be enhanced.

Other Embodiments

The present invention is not limited to the first embodiment or the second embodiment described above, and other embodiments can be adopted. For example, the combustion device according to the present invention is not limited to a water heater, which heats water for hot water supply as a target fluid, and may be a combustion device that heats, for example, a heat medium (a liquid or a gas) for heating as a target fluid. Further, a fuel of the burners 4 is not limited to a fuel gas, and may alternatively be a liquid fuel, such as kerosene. 

What is claimed is:
 1. A combustion device comprising: a burner which generates heat for heating a target fluid by a combustion operation; a fuel supply unit which supplies a fuel to the burner; a combustion fan which supplies air for combustion to the burner; and a control unit which has a function for determining a required amount of heat for temperature control of the target fluid and for controlling the fuel supply unit and the combustion fan according to the required amount of heat, wherein the control unit is configured to be capable of performing ON-OFF combustion control processing, which is processing for controlling the fuel supply unit and the combustion fan so as to intermittently perform the combustion operation of the burner, and is also configured to control the fuel supply unit and the combustion fan so as to change an amount of a fuel to be supplied to the burner and a number of rotations of the combustion fan according to the required amount of heat for temperature control of the target fluid at the time of igniting the burner to restart the combustion operation of the burner after the burner is extinguished in the ON-OFF combustion control processing.
 2. The combustion device according to claim 1, wherein the control unit has a function for detecting a degree of blockage of a supply/exhaust flow path, which is a flow path of air for combustion or combustion exhaust gas, while operating the combustion fan at a predetermined number of rotations in an extinguished state of the burner in the ON-OFF combustion control processing, and is configured to control the combustion fan so as to change the number of rotations of the combustion fan at the time of ignition following an extinguished state of the burner according to the required amount of heat for the temperature control of the target fluid and the degree of blockage in a case where at least the degree of blockage is higher than a predetermined value.
 3. The combustion device according to claim 1, wherein the control unit has a function for detecting a degree of blockage of a supply/exhaust flow path, which is the flow path of air for combustion or combustion exhaust gas, while operating the combustion fan at a predetermined number of rotations in an extinguished state of the burner in the ON-OFF combustion control processing, and is configured to control, in a case where the degree of blockage is lower than a predetermined value, the fuel supply unit and the combustion fan so as to change the amount of a fuel to be supplied to the burner and the number of rotations of the combustion fan according to the required amount of heat for the temperature control of the target fluid at the time of igniting the burner to restart the combustion operation of the burner after the burner is extinguished, and to control, in a case where the degree of blockage is higher than a predetermined value, the fuel supply unit so as to set the amount of a fuel to be supplied to the burner at the time of igniting the burner to restart the combustion operation of the burner after the burner is extinguished to a predetermined amount, and to control the combustion fan so as to set the number of rotations of the combustion fan to a number of rotations set according to the degree of blockage.
 4. The combustion device according to claim 1, wherein the control unit is configured to control, in a case where the ignition of the burner is not detected at the time of igniting the burner to restart the combustion operation of the burner after the burner is extinguished, the fuel supply unit and the combustion fan so as to increase the amount of fuel to be supplied to the burner and the number of rotations of the combustion fan as compared with the time of ignition at which the ignition was not detected.
 5. The combustion device according to claim 2, wherein the control unit is configured to control, in a case where the ignition of the burner is not detected at the time of igniting the burner to restart the combustion operation of the burner after the burner is extinguished, the fuel supply unit and the combustion fan so as to increase the amount of fuel to be supplied to the burner and the number of rotations of the combustion fan as compared with the time of ignition at which the ignition was not detected.
 6. The combustion device according to claim 3, wherein the control unit is configured to control, in a case where the ignition of the burner is not detected at the time of igniting the burner to restart the combustion operation of the burner after the burner is extinguished, the fuel supply unit and the combustion fan so as to increase the amount of fuel to be supplied to the burner and the number of rotations of the combustion fan as compared with the time of ignition at which the ignition was not detected. 